[en] For 0.25-1 MeV He²⁺-He Collision the authors have measured state selective and scattering angle dependend differential single and double capture cross sections. The experiment has been performed by measuring the momentum of recoiling ion with an accuracy of 0.26 au using cold target recoil ion momentum spectroscopy (COLTRIMS). With the same experimental technique they have clearly separated the contributions of the electron-electron and the nuclear-electron interaction to projectile ionisation for 0.5-2 MeV He⁺-He collisions

[en] The ratio, R, of cross sections for double and single ionization of helium induced by photons as a function of their energy is of particular interest as a measure of the relative importance of electron correlation effects. Calculations of this quantity are highly sensitive to assumptions about correlations between the two escaping electrons. At photon energies above ∼6 keV the major contributing process comes from Compton scattering. Recent theories differ widely in their predictions of an asymptotic value of R. The authors have made a measurement at a photon energy significantly higher than those explored previously. For this they chose the 60-keV x-ray beam at ID15 of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. To minimize background problems, they employed the COLTRIMS (Cold Target Recoil Ion Momentum Spectroscopy) technique and a supersonic cold jet of helium gas. Using a position-sensitive channel-plate detector and time-of-flight measurement, the authors were able to cleanly identify the He ions and determine a value of R. They discuss how this result serves to discriminate between several theoretical calculations of the asymptotic limit

No abstract available

[en] We have developed a novel delay-line anode design based on L/2 shifted maeander-lines for the readout of open-faced and sealed MCP-based detectors. In combination with the sealed detector (image intensifier) we are able to provide position and time sensitive single photon detection from near UV to near IR. (orig.)

[en] Vector correlation is a powerful method for the investigation of photofragmentation of molecules or clusters. It consists of measuring in coincidence the velocity vectors of the electrons and atomic fragments emitted from the same physical event, and provides detailed information about the spectroscopy and intramolecular dynamics of excited states. A new velocity spectrometer which combines imaging and time-resolved detection techniques has been developed and applied to the investigation of dissociative photoionization of diatomic molecules (NO, CO, O₂, H₂, etc.) induced by synchrotron radiation linearly polarized light (P)(AB+hν(P)→A⁺+B*+e in the VUV photon energy range (20 eV≤hν≤40 eV). The (V_A⁺,V_e) velocity vector correlation leads first to the correlation of the fragment ion and electron kinetic energies, which enables to identify and select each fragmentation process and to measure their branching ratios. The angular correlation of the ion and electron velocities for a selected process leads then to the angular distribution of the photoelectrons in the molecular frame, for each orientation of the molecular axis with respect to the linear polarization of the incident light. We illustrate the method by the recent data obtained for dissociative photoionization of NO and O₂

No abstract available

[en] New applications for single particle and photon detection in many fields require both large area imaging performance and precise time information on each detected particle. Moreover, a very high data acquisition rate is desirable for most applications and eventually the detection and imaging of more than one particle arriving within a microsecond is required. Commercial CCD systems lack the timing information whereas other electronic microchannel plate (MCP) read-out schemes usually suffer from a low acquisition rate and complicated and sometimes costly read-out electronics. We have designed and tested a complete imaging system consisting of an MCP position readout with helical wire delay-lines, single-unit amplifier box and PC-controlled time-to-digital converter (TDC) readout. The system is very flexible and can detect and analyse position and timing information at single particle rates beyond 1 MHz. Alternatively, multi-hit events can be collected and analysed at about 20 kHz rate. We discuss the advantages and applications of this technique and then focus on the detector's ability to detect and analyse multiple hits

[en] High-resolution recoil-ion momentum spectroscopy (RIMS) is a novel technique to determine the charge state and the complete final momentum vector P_R of a recoiling target ion emerging from an ionizing collision of an atom with any kind of radiation. It offers a unique combination of superior momentum resolution in all three spatial directions of ΔP_R = 0.07 au with a large detection solid angle of ΔΩ_R/4π ≥ 98%. Recently, low-energy electron analysers based on rigorously new concepts and reaching similar specifications were successfully integrated into RIM spectrometers yielding so-called 'reaction microscopes'. Exploiting these techniques, a large variety of atomic reactions for in, electron, photon and antiproton impact have been explored in unprecedented detail and completeness. Among them kinematically complete experiments on electron capture, single and double ionization in ion-atom collisions at projectile energies between 5 keV and 1.4 GeV have been carried out. (author)

No abstract available

[en] For 0.25 endash 0.75-MeV He²⁺ on He collisions we have measured total state selective double capture cross sections and cross sections differential in projectile scattering angle. For 0.25 MeV we present also state-selective scattering-angle-dependent double-capture cross sections. The projectile energy loss (the final electronic state) as well as the transverse momentum transfer (i.e., the projectile scattering angle) have been obtained by measuring the momentum vector of the recoil ion using cold target recoil ion momenum spectroscopy. The resonant transfer to the ground state is found to be by far the dominant double-capture channel. Capture to nonautoionizing excited states is smaller by about a factor of 7, and results in larger scattering angles than the ground-state double capture. copyright 1998 The American Physical Society